A prosthetic aortic conduit for replacing a root portion of the aorta and a method for manufacturing the same.
The normal internal human aortic root conduit is provided with a sinus portion which has three sinuses (bulges) which surround the aortic valve. These sinuses are called sinuses of Valsalva and are arranged so that the cross-section of the sinus portion has a generally trefoil shape. The diameter and orifice area of the root are greater at the level of the sinus, decrease slightly at the base, but significantly decrease (by 20%) at the level of the sinotubular junction (where the sinus portion connects to the ascending portion of the aorta which supports the two iliac arteries).
The sinotubular junction or sinus ridge and the sinuses of Valsalva are known to be crucial for the normal function of the aortic valve. The sinus ridge is important in causing initial fluid flow eddies inside the sinuses of Valsalva (see Bellhouse B J: Velocity and pressure distributions in the aortic valve. J Fluid Mech 1969; 37(3): 587-600 and Bellhouse B. J.: The fluid mechanics of the aortic valve. In: Ionescu M. L. , Ross D. N., Woller G. H., eds. Biological tissue heart replacement. London: Butterworth-Heinemann, 1972:32-8). During systole, the aortic valve opens and the eddy currents created prevent the leaflets of the aortic valve from impacting on the aortic wall. Then, at the end of systole, the eddy currents inside the sinuses cause the leaflets of the aortic valve to become almost closed. Furthermore, the sinus curvature is very important in sharing stress with the leaflet. It has been demonstrated that during diastole the sinus walls move outwardly (increasing its circumferential curvature by 16%) taking up part of the load placed on the leaflet. Further it is known (see (Thubrikar M. J., Nolan S. P., Aouad J., Deck D.; Stress sharing between the sinus and leaflets of canine aortic valve. Ann Thorac Surg 1986; 42(4):434-40)) that the longitudinal length of the sinus changes very little or does not change at all during the cardiac cycle. In other words during the functioning of the aortic valve the sinus moves up and down as a whole without changing its length.
The standard surgical approach in patients with ascending aortic aneurysm or dissection involving the aortic root and associated with aortic valve disease is the replacement of the aortic valve and ascending aorta by means of a composite and valved graft onto which are reattached the two coronary arteries as originally described by Bentall and de Bono in their classical paper (Bentall H. H., De Bono A.: A technique for complete replacement of the ascending aorta, Thorax 1968; 23: 338-9). The xe2x80x9copenxe2x80x9d (Carrel button) method of coronary reimplantation was later recommended to decrease the tension on the coronary ostia while minimizing the risk of late false aneurysm formation. This xe2x80x9cCarrel buttonxe2x80x9d method has already reduced the incidence of pseudoaneurysm formation mainly through the reduction of the tension on the ostial anastomoses (see Svensson L. G.; Crawford E. S.; Hess K. R.; Coselli J. S.; Safi H. J.; Composite valve graft replacement of the proximal aorta: comparison of techniques in 348 patients. Ann Thorac Surg 1992, 54(3) 427-370). A modification of the standard technique was also introduced by Cabrol et al (Cabrol C, Pavie A, Gandjbakhch I. et al: Complete replacement of the ascending aorta with reimplantation of the coronary arteries. New Surgical approach, J Thorac Cardiovasc Surg 1981: 81; 309-15) for those cases of difficult presentation (low lying coronary ostia, calcified coronary ostia, tissue fibrosis in redo cases) where the coronary ostia are reattached to the aortic conduit by interposition of a small conduit made in DACRON. DACRON is the Trade Name for a material formed from straight chain polyester; the material may also be known as TERYLENE.
If the aortic valve leaflets are normal, a valve-sparing aortic root remodelling procedure which keeps the natural patient valve on site is a reasonable alternative in certain individuals. David and Feindel (David T. E., Feindel C. M.: An aortic valve-sparing operation for patients with aortic incompetence and aneurysm of the ascending aorta, J Thorac Cardiovasc Surg 1992; 103(4): 617-21) described a surgical technique where the dilated aortic root is replaced with a tube made of DACRON fibres and the native aortic valve is integrated within the graft. This method is generally known as the xe2x80x9cTirone David Type I aortic valve sparing procedurexe2x80x9d. However, the lack of sinuses in a straight tube graft was found to negatively influence proper valve function, with the consequent risk of decreasing valva longevity (Kunzelman K. S., Grande K. J., David T. E., Cochran R. P., Verrier E. D. : Aortic root and valve relationships. Impact on surgical repair J Thorac Cardiovascular Surg 1995; 109(2): 345-51).
Thus in the Tirone David Type I technique for valve sparing operations, the use of a straight tube without a sinus component raises several problems: opening and closing of the native valve is not optimal. For example, upon valve opening, the leaflets might impact on the graft and be potentially damaged. The absence or delay in eddy current formation might alter valve closure causing some regurgitation. Furthermore, the diastolic stress is borne only by the leaflet and is not shared with the sinuses causing a potential decrease in leaflet longevity.
An optimal design for root replacement should therefore incorporate sinuses and a sinotubular junction and further refinement of the technique consisted of trimming one end of the aortic tube graft to produce three separate extensions designed to replace the three sinuses. The reshaped DACRON tube was then sutured to the aortic valve remnants (see David T. E., Feindel C. M., Bos J.: Repair of the aortic valve in patients with aortic insufficiency and aortic root aneurysm. J Thorac Cardiovasc Surg 1995; 109(2) :345-51) to obtain a final configuration resembling more closely the native aortic root. A similar technique was also described by Yacoub el al (Saram M. A., Yacoub M.: Remodeling of the aortic valve annulus. J Thorac Cardiovasc Surg 1993; 105(3): 435-8) several years previously.
In U.S. Pat. No. 5,139,515 it was proposed to provide an aortic graft having a lower portions provided with xe2x80x9cbulgesxe2x80x9d apparently mimicking the sinuses of Valsalva. However no method to produce such a conduit for use in aortic surgery is described in the patent. U.S. Pat. No. 5,139,515 described a conduit having an xe2x80x9cannular wall of a crimped material similar to that of conventional prosthesisxe2x80x9d. No indication is actually given of how to obtain the xe2x80x9cannularly-spaced radially outward bulgesxe2x80x9d mimicking the sinuses. Moreover the drawings clearly show that the conduit, including the sinus portion, is provided along its whole length with corrugations which lie perpendicularly to the longitudinal axis of the prosethesis, and which impart longitudinal elasticity to the whole of the conduit. Upon implantation, the graft cannot expand radially outwardly, but has the potential to move and extend in the longitudinal direction of the longitudinal axis of the prosthesis.
Therefore there is still a need for an effective prosthetic conduit to replace the aortic root while providing all the advantages of the natural sinuses of Valsalva.
It is therefore one of the objects of the invention to provide a prosthetic aortic conduit which overcomes the drawbacks mentioned above and which upon implantation has the ability to expand radially outwardly whilst maintaining a degree of flexibility in the longitudinal direction.
It is another object of the invention to provide a conduit which is specifically designed to closely mimic the sinuses of Valsalva.
A first object of the invention is a prosthetic aortic conduit for replacing a root portion of an aorta which comprises a first tubular portion and a second tubular portion connected together along a substantially common axis. The second tubular portion does not substantially deform in a longitudinal direction and has resilient means which allow said second portion to be expandable in a lateral direction. As the second portion is able to deform laterally it is able to mimic the function of the sinuses of Valsalva.
It is preferred that the first tubular portion of the prosthetic aortic conduit of the invention be provided with resilient means which allow expansion of said first portion in a longitudinal direction.
It is also preferred that the prosthetic aortic conduit be made of polyester or PTFE material, including expanded PTFE material which may optionally be coated. A preferred material is DACRON.
It is further preferred that the second portion resilient means comprises longitudinally extending corrugations.
It is further preferred that the first portion resilient means of the conduit of the invention comprises annular corrugations successively provided along the longitudinal axis of said conduit.
It is further preferred that the first and second portions of the conduit be made of two distinct tubes which are secured together along said common axis.
It is further preferred that the conduit is provided with a third tubular portion which is connected to the second portion along the substantially common axis of the conduit. Advantageously this third tubular portion is provided with resilient means which allows expansion of said third portion in a longitudinal direction.
Optionally the conduit of the invention may be further provided with a prosthetic valve.
Another object of the invention is a method of manufacturing a prosthetic aortic conduit as described above. This method comprises the following steps:
a) providing a first tubular conduit suitable for use in heart surgery, the first conduit having a longitudinal axis and first resilient means allowing some expansion in the longitudinal direction only; and
b) securing to one of the ends of this first conduit a second tubular conduit suitable for use in heart surgery so that the lumens of the first and second conduits are aligned and are continuous, the second conduit having a longitudinal axis and second resilient means which allows some expansion in the lateral direction only.
It is preferred that the first resilient means comprises a plurality of annular corrugations successively provided along the longitudinal axis of the first conduit and that the second resilient means comprises a plurality of longitudinally extending corrugations successively provided around the circumference of the second conduit.
It is also preferred that the second tubular conduit be made according to following steps:
a) taking a tubular conduit suitable for use in heart surgery, such conduit having annular corrugations allowing some expansion in the longitudinal direction only and having two opposite ends; and
b) cutting said tubular conduit from end to end; and
c) aligning and securing the two opposite ends together to obtain said second tubular conduit.
Where a third tubular conduit is required, this will simply be attached to the end of the second conduit which is not attached or not intended for attachment to the first conduit. Again the lumen of the third conduit should be commonly aligned with that of the second conduit. Optionally the third conduit may be attached to the combination of the first and second conduits. Alternatively the third conduit may be attached to the second conduit and then the first conduit attached. As described above, the third conduit will have circumferentially extending corrugations so will be similar to the first conduit in construction, but will generally be of a shorter length.
It is further preferred that the first, second and third tubular conduits are made of DACRON or PTFE material.